The invention relates to a charge-coupled device of the buried channel type comprising a semiconductor body having a charge transport channel of the one conductivity type, which is located near a surface and passes via a pn junction into an adjoining layer of the second conductivity type opposite to the first conductivity type, the surface being provided with a series of successive electrodes, which are separated from the surface by an isolating layer and are connected to a voltage source for applying clock voltages having a blocking level and an active level, while in the charge transport channel a potential barrier or a potential well is induced, the blocking level being chosen so that inversion of the conductivity type occurs at the surface of the semiconductor body.
The invention further relates to an image sensor arrangement comprising such a charge-coupled device. The information can be supplied both electrically, i.e. from an external electric source via a separate input stage, and optically, the charge carriers being generated by absorption of incident radiation in the semiconductor body itself. In the former case, the charge-coupled device can be used as a memory or as a signal processor, while in the latter case it can be used as an image sensor or a sensor in a camera.
A charge-coupled device of the kind described in the opening paragraph is known inter alia from the article by N.J. Saks "A Technique for Suppressing Dark Current Generated by Interface States in Buried Channel CCD imagers", published in I.E.E.E. Electron Device Letters, Vol. ED-1, No. 7 (July 1980), pp. 131/133.
In charge-coupled devices, the leakage current or dark current is kept as low as possible. With the use of the device, for example, as a memory, the leakage current determines to a great extent the maximum storage time. In charge-coupled image sensor arrangements, the sensitivity is limited to a considerable extent by the dark current of the CCD. In general, as is know, a large part of the dark current is caused by surface states in the forbidden energy band. These states are used by the electrons as intermediate station when passing from the valency band to the conduction band. A considerable reduction of the dark current in CCD's can be attained in that these surface states are freed via recombination with holes from electrons before they have made the second step to the conduction band. A method suitable for this purpose consists in bringing the surface into inversion, as a result of which this surface is overflown with holes, as described in the aforementioned publication. This known arrangement is a CCD image sensor, in which during the integration period such a voltage is applied to the electrodes that the whole surface of the transport channel is in inversion. A disadvantage is that also the semiconductor surface below the integrating electrodes is in inversion. The charge separating function of the electrodes--usually by application of different voltages to the electrodes--is practically entirely eliminated due to the fact that the surface potential is practically entirely determined by the potential in the inversion layer. As already indicated in the publication, the separation between the successive charge packets should then be obtained in a different manner.